Yale study finds the number of trees on the planet higher than expected

By Register Staff

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1:35 pm EDT, Wednesday, September 2, 2015

The fall view from East Rock Park in New Haven shows a well treed city

The fall view from East Rock Park in New Haven shows a well treed city

Photo: Journal Register Co.

Photo: Journal Register Co.

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The fall view from East Rock Park in New Haven shows a well treed city

The fall view from East Rock Park in New Haven shows a well treed city

Photo: Journal Register Co.

Yale study finds the number of trees on the planet higher than expected

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NEW HAVEN >> There are a lot of trees covering the Earth, 3 trillion in fact, but there are only half as many as our earliest ancestors could have enjoyed.

The new count — to be more precise, that’s 3.04 trillion — by Yale University-led researchers is 7.5 times higher than some previous estimates, according to a release, almost 422 for each of the Earth’s 7.2 billion people. But it’s just 54 percent of the number that existed when Homo sapiens first took a walk in the shade.

“Trees are among the most prominent and critical organisms on Earth, yet we are only recently beginning to comprehend their global extent and distribution,” said Thomas Crowther, a postdoctoral fellow at the Yale School of Forestry and Environmental Studies, in the release.

“They store huge amounts of carbon, are essential for the cycling of nutrients, for water and air quality, and for countless human services. Yet you ask people to estimate, within an order of magnitude, how many trees there are and they don’t know where to begin. I don’t know what I would have guessed, but I was certainly surprised to find that we were talking about trillions.”

Crowther was lead author of the study, which included researchers from 15 countries and which appears in the journal Nature. They used satellite imagery, inventories of forests and supercomputing to map the numbers of trees per square kilometer worldwide. The more accurate number will help in predicting climate change and determining the distribution of plants and animals.

“The study of Crowther et al. moves us towards a needed direct quantification of tree distributions, information ready to be used by a host of downstream science investigations,” said Matthew Hansen, a global forestry expert from the University of Maryland who was not involved in the study.

The highest densities of trees were found in sub-arctic forests in Russia, Scandinavia and North America. But the largest forests are in the tropics, where 43 percent of the world’s trees grow.

The study found that trees grow better in wetter climates, but those some of those areas also draw more humans, who want to cut down the trees to grow food. Overall, the more human activity, the less dense are the trees. Deforestation, changes in land use and forest management cost the planet more than 15 billion trees each year, the study found.

“We’ve nearly halved the number of trees on the planet, and we’ve seen the impacts on climate and human health as a result,” Crowther said. “This study highlights how much more effort is needed if we are to restore healthy forests worldwide.”